The present invention relates to an apparatus for producing semiconductor devices by, for example, etching, heating and rinsing materials to be treated such as semiconductor wafers.
In the case of etching aluminum layers on wafers or materials to be treated, chloride gases such as SiCl.sub.4, CCl.sub.4, BCl.sub.3, Cl.sub.2 have been generally used. Etching proceeds by the chemical reactions of Al with these etching gases. In the case of a sheet type etching process in which wafers are processed or etched one at a time, an etching chamber must be always maintained in a vacuum state in order to prevent corrosion by chlorine produced by the chemical reactions of water in the atmospheric air with the etching gases.
Furthermore, after the etching process, when the etched wafers are exposed to the surrounding atmosphere, corrosion occurs so that the etched wafers are subjected to the heat-treatment or water rinsing, thereby removing residual chloride compounds.
However, in the prior art apparatus for producing semiconductor devices, an etching unit is disposed independently of post-treatment units so that a large space is required for the installation of the whole apparatus for producing semiconductor devices. Furthermore, the etched wafers are corroded because it takes a long period of time to transfer the etched wafers from the etching unit to the post-treatment unit.
Recently, a fully automatic apparatus for producing semiconductor devices has been developed so that a wafer is automatically transferred through a plurality of treatment chambers for various treatments in a vacuum from a load cassette to an unload cassette without requiring any manual handling of wafers, whereby the treatment time is shortened and the attachment of dust or contaminants on the wafers is avoided.
However, with the apparatus of the type just described above, when wafers are contaminated with dust, abnormal etching results so that the reliability and yield of the finished wafers are decreased. It is believed that dust is introduced because of the friction between moving parts of the apparatus, foreign matter entrained in the gases introduced and the products of chemical reactions. Therefore it becomes very important to find out where wafers which are transferred through a plurality of treatment chambers are contaminated with dust.
However, in the case of the prior art apparatus for producing semiconductor devices, it is only possible to detect the quantity of dust attached to a wafer only after this wafer has been discharged out of the last one of a plurality of treatment chambers. That is, it has been impossible to detect the quantity of dust attached to a wafer in one particular treatment chamber.
In the case of the prior art etching devices employing fluoride etching gases, when the etched wafer is discharged out of the etching device, corrosion of the wafer occurs because of the chemical reactions between the oxygen in the surrounding atmosphere and the chloride etchant such as AlCl.sub.3 still remaining on the wafer.
In order to overcome this problem, there has been proposed an apparatus for producing a semiconductor device in which a cassette holding a plurality of etched wafers is placed into an electric furnace or a case with an industrial dryer so that the etched wafers are subjected simultaneously to the heat treatment process.
More specifically, as shown in FIG. 1, a partition plate b formed with a plurality of holes is disposed in a case a so that the case a is divided into an upper chamber and a lower chamber. A cassette c holding a plurality of wafer d is placed upon the partition plate b and the case a is air-tightly closed with a cover e. The wafers d are dried by the hot air discharged from dryers f disposed on the top of the case a and the hot air flows through the holes of the partition plate b and then is discharged through a discharge port g formed at a lower portion of one side wall of the case a into the surrounding atmosphere.
With the device of the type just described above, some portions of wafers are not sufficiently heated because of the cassette c so that it takes a long period of time before the cassettes d are elevated to a predetermined temperature. Furthermore, there is the problem that the wafers d are not uniformly heated so that the variations in properties of wafers result in the post-treatment processes.
Furthermore the device of the type described above is of the batch type because the cassette c holding a plurality of wafers d is placed into the device. However, such a batch type heat-treatment device cannot be directly connected to an etching device.
Meanwhile, recently in the production of semiconductor devices, there has been a strong increasing demand for a higher packaging density and a higher rate of production. Therefore, there has been employed a reactive ion etching process which can etch extremely fine elements and can obtain the vertical side walls without undercuts.
For instance, in the case of etching aluminum which has been widely used as a material for defining conduction paths between electrodes, the chloride gases are used. That is, a semiconductor wafer is charged placed into a reaction vessel and then the reaction vessel is evacuated so that the glow discharge is produced in the reaction gas atmosphere. Then the reaction between a material to be etched on the wafer and the etching gases proceeds so that the material to be etched is changed into a volatile chemical compound. In this manner, the etching process proceeds.
When the etching process is completed and the etched wafer is discharged from the reaction vessel into the surrounding atmosphere, the etched wafer still includes the etching gases. As a result, the chemical reactions proceed between these remaining etching gases and the water in the surrounding air so that a conductor pattern of the material not etched and remaining on the wafer is connected to another conductor pattern. As a consequence, the conductor paths are broken and short-circuited.
It follows therefore that it is imperative to remove the reaction gases still remaining on the etched wafer immediately after the completion of the etching cycle. This process can be very effectively accomplished by blowing the hot air against the etched wafer and/or heating the etched wafer. Therefore, the etched wafers are heated in an electric furnace or by an industrial dryer, but such heating takes a long period of time to heat the etched wafer to a predetermined temperature; a uniform temperature distribution cannot be attained so that the properties of the heat-treated wafer vary; and it takes a long period of time before the etched wafer is subjected to the heat-treatment.
In order to overcome the above and other problems, there has been proposed a heat-treatment device which can be directly connected to an etching device. A wafer etched in the etching device is immediately transferred by a conveyor or the like from the etching device into the heat-treatment chamber in which the transferred wafer is immediately subjected to the heat-treatment process by means of a normally heated heating plate and an air-heating device. However, since the conveyor or the like is extended into the heat-treatment chamber, a drive means for driving such conveyor or the like from the exterior of the heat-treatment chamber is needed. Therefore, a power transmission means must interconnect between the exterior driving means and the conveyor or the like in the heat-treatment chamber through a hole formed through one side wall thereof. As a result, the hot gases are discharged out of the heat-treatment chamber through this hole into the surrounding atmosphere so that the operations of various devices disposed adjacent to the heat-treatment chamber are adversely affected by the temperature rise. Furthermore, corrosion of these peripheral devices results because the discharged gases contain the reaction or etching gases.
Therefore, it may be proposed to dispose the complex driving means for driving the conveyor or the like within the heat-treatment chamber. However, it is impossible to do so because the driving means is exposed to high temperatures and the reaction gases within the heat-treatment chamber causing corrosion of the driving means. As a consequence, the driving means must be minimized as much as possible and the conveyor system or the like must be simplified as much as possible. Therefore, a belt conveyor is employed. Since a wafer is transported by the belt conveyor, it cannot come into direct contact with a heating plate. As a result, the wafer heating efficiency is considerably low, and positive and fast heat-treatment cannot be accomplished.
In the RIE device (Reactive Ion Etching device) which is one of the types of plasma etching devices, a pair of parallel electrodes are disposed within a vacuum vessel into which an etching gas is introduced, and a wafer is securely held in position on one of the electrodes. RF power is applied to one of the electrodes so that the plasma is produced, whereby the wafer is etched.
However, when the vacuum vessel is made of stainless steel and a chloride etching gas is introduced into the vacuum chamber, iron, nickel and chromium are discharged out of the vacuum vessel so that the wafer is contaminated and the properties or characteristics of the wafer are considerably degraded.
In order to overcome the above problem, the vacuum vessel is made of alumina or the inner aluminum surfaces of the vacuum vessel are oxidized. However, since alumina is very expensive and has low strength, it is not preferable to use it to fabricate a vacuum chamber.
Furthermore, the commpounds resulting from the etching process tend to attach themselves to the inner surfaces of the vacuum chamber so that in order to prevent the adverse effects of such compounds on the wafer, the interior of the vacuum chamber must be frequently cleaned. However, with the prior art vacuum vessels, cleaning and maintenance are difficult.